Field
The following relates, in one aspect, to systems and methods for transferring metadata from one device to another over standard AudioVideo (AV) interfaces.
Related Art
Transmission of AV data from a source device to a sink device is typically implemented according to a pre-defined standard. Providing a standard for communication of such data allows source and sink devices to be built to the standard by different entities and have an expectation that those devices will be able to be used together.
For example, High Definition Multimedia Interface (HDMI) provides a standard that is widely adopted and used in devices for AV data communication. HDMI implements EIA/CEA standard video formats and waveforms. Digital video signals can be broken into three main parts: the vertical blanking region, the horizontal blanking region, and the active picture region. The vertical blanking region contains the vertical sync pulse that signifies a new field or frame (field and frame are used interchangeably herein, unless explicitly indicated otherwise). There are multiple lines of video data in each field.
For example, a Full High-Definition (HD) 1080p/60 Hz video stream has a vertical blanking interval every 16.67 ms (60 Hz) to signify a new frame and a horizontal blanking interval every 14.8 μs to signify a new horizontal line. Within the 14.8 μs horizontal line duration there are 2,200 pixels, which include the horizontal blanking period and the active picture. This requires a pixel clock of 148.5 MHz (1/14.8 μs horizontal line duration*2,200 pixels) to generate the video frame composed of the three regions.
The active picture region is the location of the pixels that a user would see on the display. The pixel color value is stored in three channels that are typically RGB- or YUV (YPbPr)-encoded. The color levels can be encoded in a defined number of bits per channel, such as from between 6 to 16 bits per channel, meaning that each pixel has a 24- to 48-bit color value. A digital monitor communicates Enhanced Display Identification Data (EDID) to a source, in order to describe what video formats and timings that monitor supports.
Information about a current video format is communicated from a source to a sink. In HDMI, a video format is indicated as a standard VIC code in an InfoFrame. An InfoFrame is a packet of data that is provided in a vertical blanking interval (IE: in a period where the video signaling indicates that there is no active video data). Resolution also can be communicated via other mechanisms, such as a DCDB record (as in SuperMHL).
For example, FIG. 1 shows a timing diagram that illustrates how audio and video data are transmitted and timed relative to each other for a frame in HDMI. FIG. 1 depicts an active video area 110, an area containing audio sample packets 115, and unused blanking areas 120a and 120b. FIG. 1 also depicts that part of the blanking area, e.g., blanking area 120a can be filled with infoframe and data island packets. HDMI interleaves video, audio and auxiliary data using three different packet types, called the Video Data Period, the Data Island Period and the Control Period. During the Video Data Period, the pixels of an active video line are transmitted. Data Island packets can be transmitted in a pre-defined location 122 within a blanking interval used for Infoframe and data island packet transmission.